The longer-term goal of our research effort is to understand why persons with addictions change their social networks in either positive or negative ways, and how important health outcomes and health behaviors affect are influenced by social changes. Our research focuses on persons with addictive disorders because addiction can have strong, even catastrophic, effects on our strongest social ties. On the other hand, there is substantial evidence, including new analyses we present, that social relationships are a strong determinant of addictions outcome. Since addictions are chronic, relapsing disorders, if we were able to promote durable healthy relationships for addicts, these relationships might reduce the need for costly and not always accessible professional services. Unfortunately, we lack a basic understanding of why people change their social relationships, for better or for worse. Our research will illuminate the processes of change in addicts' social networks. We will recruit 300 persons from addictions treatment facilities and follow them naturalistically for two years, gathering intensive longitudinal data on social relationships, substance use, and other variables. Our study has three aims: (1) To determine how a person's relationships are affected by other relationships, and by substance use, co-varying for relationship type and history; (2) To replicate and extend prior research on the effects of social network characteristics on substance use outcome; and (3) To determine social network influences on entry into substance abuse treatment, and mutual-help participation. Cox proportional hazards regressions and hierarchical linear models with time varying covariates will be used to test the a priori predictions laid out i the proposal. PUBLIC HEALTH RELEVANCE: There is compelling evidence that social relationships are a strong determinant of future substance use, in both positive and negative ways. Treatment programs could benefit from being able to take maximum advantage of positive relationships, while minimizing the consequences of negative ones. However, we lack basic knowledge about why persons with addictions change their social relationships in either direction; this study is designed to produce some of that basic knowledge.